Electronic devices exist in the art for outputting virtual reality (VR) images or three-dimensional (3D) images. As technology has improved, these electronic devices have been made lighter and smaller. Examples of these electronic devices include smart glasses, head mount devices (hereinafter, referred to as HMDs), or the like.
For example, an HMD may be worn on a user's head. The HMD may display a screen in front of the user's eyes and may output a 3D image. The HMD may provide a variety of augmented reality (AR) effects or virtual reality (VR) effects.